Email Subject Line Analysis: How Well Do Popular Terms Fare?

August 4, 2015

This article is included in these additional categories:

B2B | Content Marketing | Digital | Email | Featured | Financial Services | Media & Entertainment | Retail & E-Commerce | Trade Shows & Events

Adestra-Retail-B2C-Email-Subject-Line-Keyword-Performance-Aug2015Adestra has released [download page] its latest email subject line report [download page], analyzing a host of keywords and phrases across 4 sectors to see their relative lift or decline against the industry sector average. The study is based on a large sample of more than 125,000 individual email campaigns, 3 billion attempted sends, 400 million opens and 55 million clicks.

Before the results, the requisite disclaimers. As Adestra notes, “any single word won’t always work for everyone all the time.” Also, while Adestra works with global brands (particularly media and publishing companies) covering Europe, Asia, and the US, the majority of sends analyzed are UK-related, so it’s possible that there are geographical variances in response to the terms analyzed.

Looking at the top and bottom 10 terms of the hundreds examined across industries, it’s worth noting that “Thanks” and “Thank you” both appear in the top 10. Typically used in automated, transactional email, these speak to the above-average response rates to triggered emails.

Meanwhile, content-related terms pepper the bottom 10, including “subscription,” “report,” “intelligence,” “whitepaper,” and “journal.” As Adestra reminds, “your customers still buy benefits, not features.”

Following is a brief look at how some of the more popular terms used fared, by industry sector. The study – available here – lists out all the results for the full 300 keywords analyzed and is certainly worth a read.


Emails offering discounts and free shipping sit atop retailers’ most effective digital promotional vehicles, and MarketingCharts research into consumers’ email behavior similarly finds that emails advertising discounts are most likely to spur email opens. So which discounts levels work best?

Here’s what Adestra found (see the chart leading off this article): “10% off” (+7%) and “25%” (+3%) off emails showed above-average open rates, while “15% off” (-2%) and “50% off” (-7%) terms had below-average rates. However, click rates were above-average for all of those discount levels, most notably for “50% off” (33%), “25% off” (21%) and “10% off” (21%) emails. Apparently there’s some level of distrust for “15% off” or it’s too particular a number for email recipients? To confuse matters some more, “15% off” performed best in terms of unsubscribe rates relative to the sector average, though “25% off” and “50% off” terms also had below-average unsubscribe rates. In sum, “25% off” was the only discount level to be in the green (perform better than average) for each metric.

One other note: personalized emails fared far worse than average in open (-30%), click (-20%), and unsubscribe (+9%) rates, a finding in apparent contradiction to previous research on the topic.

Conferences / Events

Adestra-Conf-Event-Email-Subject-Line-Keyword-Performance-Aug2015Optimizing email subject lines in the conferences and events sector is important, as data contained in MarketingCharts’ 2015 B2B Digital Marketing Insights Report shows that an email invite from an event organizer carries as much weight as as a personal invite from an exhibitor when attendees are selecting an exhibition to attend.

In analyzing the most popular terms in the conference and events industries, Adestra once again notes that those associated with features rather than benefits have below-average response rates. This is true for “agenda,” “forum,” “keynote,” and “speakers,” all of which had below-average open rates (13-22% below average) and click rates (ranging from 36% below to a stunning 259% below-average rate, for “keynote”). The word “advice,” though, was associated with a slightly above-average open rate (+6%) and a more significant rise in click rate (+27%).

Among call-to-action terms, “buy” and “save” both demonstrated above-average open and click rates, while more commonly-used terms such as “come,” “early bird,” “free,” and “register” were below-average in each metric.

Media and Publishing

Adestra-Media-Publishing-Email-Subject-Line-Keyword-Performance-Aug2015The Adestra report finds that “strong editorial content, when used as a hero topic in the subject line, drives huge response across all metrics.” Specifically, the study highlights the following popular terms:

  • Breaking (35% above-average open rate; 66% above-average click rate);
  • Exclusive (15% above-average open rate; 7% above-average click rate);
  • Review (24% above-average open rate; 61% above-average click rate);
  • Top stories (28% above-average open rate; 58% above-average click rate);

Popular subscription-related terms, however, didn’t always fare as well. The term “25% off” – a winner in the retail context – was linked to a 7% below-average open rate and a 65% below-average click rate. “Discount” also fared similarly, while “free” and “order today” did well in one metric but not the other. The only term highlighted to perform well was “on sale now,” which registered a 27% above-average open rate and a 57% above-average click rate.

B2B / Professional Services / Financial

Adestra-B2B-Prof-Fincl-Email-Subject-Line-Keyword-Performance-Aug2015White papers might be effective content assets in the awareness and consideration phases of the buyer journey (see MarketingCharts’ B2B report), but Adestra’s analysis suggests that marketers stay away from using them in their email subject lines. In fact, subject lines with the term “whitepaper” had open rates 208% lower than the sector average, and click rates an even more dismal 402% below the sector average. Similarly, the terms “alert” (-105% and -353%, respectively) and “forecast” (-149% and -270%, respectively) are linked to poor response rates. While “download” and “report” had below-average response rates, they hewed closer to the average.

The only popular term of those identified to have above-average open (+33%) and click (+40%) rates was “news.” Adestra theorizes that with B2B product offerings often being complex and involving long sales cycles, “the consistent provision of news items is pivotal to long-term success.”

Finally, in comparing some other popular terms for their impact on unsubscribe rates, the report indicates that “bulletin,” “interview” and “industry” perform well, while “asset” and “discount” increase unsubscribe rates.

About the Data: Adestra notes in its report that in order to deliver “a measure of statistical reliability, we treated each keyword’s probability of success as a binomial variable. Then, we standardized each keyword and determined 95% two-tailed confidence intervals.” These intervals are displayed for each keyword, with the interpretation being that “if you were to use this keyword in your subject line, 95% of the time the results will fall within the confidence interval bands.” More methodological details and results are available in the report, which is accessible here.

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